The present invention relates to a circuit for piloting an inductive load, particularly for the operation of an electro-injector for Diesel-cycle internal combustion engines.
More specifically, the invention relates to a circuit comprising
a low-voltage supply, PA0 reactive circuit means including an energy-storage inductor, PA0 control circuit means including PA0 a first controlled switch for connecting the supply to the inductor to effect a storage of energy, and PA0 a second controlled switch for causing the connection of the reactive circuit means to the load and rapid discharge into the load of the energy stored in the inductor, so as to inject a current pulse into the load.
A circuit of this type is described in Italian patent application No. 67953-A/85. This known circuit comprises a plurality of circuit branches, each of which has a capacitor connected in parallel with an inductive load to form a resonant circuit with the load. The rapid transfer of current into each of these loads is achieved by first storing energy provided by the supply in the storage inductor and then connecting the storage inductor to the resonant circuit including the load to be energized. The control solenoids of the electro-injectors for Diesel engines represent non-linear inductive loads with a relatively small inductance.
For optimal and precise control of injection in a Diesel engine, the activation times for individual injectors must be precisely controllable. For this purpose, it is particularly necessary that the rise time of the current in the control solenoid of the electro-injector which is to be activated from time to time is extremely small, and less than the minimum injection time by at least one order of magnitude. It is also necessary that, at least in the initial stage of excitation, the current not only reaches a high value, but also that the integral of the current (linked to the force developed on the movable armature of the electro-injector control solenoid) is consistent. In other words, once the peak value has been reached the current in the load must remain at high levels, of the order of the peak value, for some time.
Known circuits of the above-specified type enable quite small rise times of the current in the load to be obtained; however, given the structure of such circuits, it is inevitable that energy will be transferred from the load back to the reactive energy storage and discharge circuit means thereof. In particular, in such circuits, once the current in the load has reached the peak value, it decays, tending towards the value defined purely by the resistive components of the circuit, with a time constant to whose definition the storage inductor also contributes.
In practice, when the peak value is reached, the current in the load decays with a smaller time constant and therefore more rapidly, the faster the current rises to its peak value.